One more hot day a week means more ER visits. Medicare Advantage members pay most.
An analysis of insurance claims from 2016 to 2023 found extreme heat consistently drove up emergency department use and cost across commercial, Medicaid, and Medicare Advantage plans.
A study published this month in Health Affairs puts a dollar figure and a claims-data trail behind a pattern climate-health researchers have described for years: extreme heat sends more people to the emergency room, and someone has to pay for it [s1].
What the study did
Researchers used health insurance claims spanning 2016 to 2023 from a large national insurer, combined with national temperature and humidity data, to run a regression analysis of how extreme heat exposure related to emergency department, inpatient, and outpatient use and cost [s1]. The analysis covered three distinct populations: people with commercial insurance, people with Medicaid, and people enrolled in Medicare Advantage [s1].
What an extra hot day does to health-system use
The study's central finding: one additional day within a given week where the heat index reached 100°F or hotter was associated with increased emergency department use and cost across nearly all of the coverage populations and age groups studied [s1]. The effect wasn't confined to emergency visits. Extreme heat was linked to significant increases in inpatient use specifically among children with commercial coverage, where it rose 1.4% [s1]; among adults ages 18 to 64 with Medicaid coverage, up 0.47% [s1]; and among Medicare Advantage members, up 0.5% [s1].
Not every category moved. The study found no statistically significant increase in inpatient cost for any of the population groups, despite the rise in inpatient use [s1]. And extreme heat was not associated with increased outpatient use or cost in any group studied [s1] — suggesting the heat-driven burden concentrates specifically in emergency and inpatient care rather than spreading across the health system broadly.
Who bears the biggest cost
Among the three populations, Medicare Advantage members had the highest annual cost attributable to extreme heat [s1]. That finding lines up with what's already understood about heat vulnerability: older adults face a higher baseline risk of heat-related complications — from cardiovascular strain to kidney injury to worsening of chronic conditions — than younger, generally healthier populations, and Medicare Advantage plans by definition cover people 65 and older or with qualifying disabilities.
Why this matters beyond the balance sheet
The study's authors frame their findings as evidence relevant to population health management, seasonal preparedness planning, and policy decisions aimed at reducing heat-related illness and its downstream costs [s1]. Unlike mortality counts, which capture only the most severe outcomes, this claims-based approach captures a wider slice of heat's health impact — the emergency visits and hospitalizations that don't make it into a fatality count but still represent real harm and real cost, borne differently depending on who's covering the bill.
What the study doesn't establish
The analysis is observational, built on historical claims and weather data rather than a controlled comparison, so it demonstrates an association between heat exposure and health-system use rather than proving a single, uniform causal pathway for every case counted. It also draws on one large national insurer's data, which may not generalize precisely to every regional insurance market or to the uninsured population, whose heat-related health-system use isn't captured in commercial or Medicare Advantage claims at all. And the 2016–2023 study window predates this year, so it describes a historical relationship between heat and cost rather than a forecast of what any specific 2026 heatwave will cost [s1].
Sources
- Extreme Heat, Health Care Use, And Costs: Evidence From Commercial Insurance, Medicaid, And Medicare Advantage — Health Affairs, 2026-04-23
Sources
- Extreme Heat, Health Care Use, And Costs: Evidence From Commercial Insurance, Medicaid, And Medicare Advantage — Health Affairs , April 23, 2026
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